[Kenth]

Are these rods fine or should i look for another set?

[steve25]

That's from heating them to press the pin in and getting them hotter then needed to get that job done!

Now the Rods temper in that area has been changed and it's surface layer will be more proned to cracking.

Is such a issue? I guess it depends on the motors stroke ( G force loads ) and intended rpm range.

I myself would not chance using them in a motor of 4.210" stroke or greater at anything more then 6800 rpm.

[Cliff R]

They're junk, I'll give you $10 for them and you pay the shipping!

Seriously, I've seen that sort of thing many times, and to date haven't seen any break in that area..........

[track73]

"At 480 degrees F., the steel turns brown, at 520 degrees, it turns purple, at 575 degrees, it turns blue and at 800 degrees, it turns grey. ... At 2000 degrees, the steel will be bright yellow."
I don't think 520-575 degrees will hurt them.

[STEELCITYFIREBIRD]

I've hung thousands of interference fit piston sets.
Coloring in that area seemed to vary on surface prep(shot peened or glass beaded) and how clean when hung. Yes temp also is surely a factor.
NONE ever came back broken, many were budget circle track motors that got their neck twisted tight... for extended periods of time and comparably heavy slugs, longer strokes.
Seems strange they are not bushed rods.
I'd use them, glass bead if you don't like seeing the color!

[steve25]

575 F is only 475 degrees away from the temperature that 4340 steel is tempered at, just sayin!

[mgarblik]

Originally Posted by STEELCITYFIREBIRD

I've hung thousands of interference fit piston sets.
Coloring in that area seemed to vary on surface prep(shot peened or glass beaded) and how clean when hung. Yes temp also is surely a factor.
NONE ever came back broken, many were budget circle track motors that got their neck twisted tight... for extended periods of time and comparably heavy slugs, longer strokes.
Seems strange they are not bushed rods.
I'd use them, glass bead if you don't like seeing the color!

Well, the shop didn't do you any favors overheating the small ends that much to put the pins in, but it is common. Have seen plenty of SBC and some Pontiac cast rods all blue from the factory. SBC small ends dipped in copper to resize and then blue on top of that from the factory. Bottom line, this being the street section, I wouldn't get too excited about it. If it was a race engine, it would have floating pins anyway. I can't honestly say I have seen one release the pin or break the rod because it was blue. As mentioned, if it was heated with oil on the surface, they turn blue at a low temperature. If the rod and pin swing smoothly in the piston bore, I would oil it up and put it together.

[NeighborsComplaint]

Unfortunately, this is the norm with most shops that do not first take the time to pin-fit the the rods to .001" interference fit. If they did, very little heat is required required to expand the small end of the rod. It's not going to hurt anything.

[Dragncar]

You want them to be more brown than blue. A good weld is also brown with proper heat.

[Brian Baker]

I saw a set of used Eagle forged rods at a swap meet for sale once that were blued like this...ON THE BIG END !!!...some kid was looking at them and when the seller wasn't around I told the kid I wouldn't buy them, telling him they got very hot for some reason, most likely from improper clearances.

[P@blo]

Originally Posted by Brian Baker

I saw a set of used Eagle forged rods at a swap meet for sale once that were blued like this...ON THE BIG END !!!...some kid was looking at them and when the seller wasn't around I told the kid I wouldn't buy them, telling him they got very hot for some reason, most likely from improper clearances.

Cool story Brian was that kids name Pamela Harris? If It were i would have suggested otherwise

I went with floating on my new set of eagle H-beam to avoid this type of situation myself Kenth.

[Gary H]

I'd have no problems running the rods as long as the pin moves freely in the pistons.

[Brian Baker]

LOL, no...but the guy selling the rods was well known in the Pontiac racing community in Maryland (and surrounding areas). His engines always ran like a scalded cat but for some reason the ones he built for others had a tendency for failure. And no, I'm not talking about JG.

Originally Posted by P@blo

Cool story Brian was that kids name Pamela Harris? If It were i would have suggested otherwise

I went with floating on my new set of eagle H-beam to avoid this type of situation myself Kenth.

[track73]

Originally Posted by steve25

575 F is only 475 degrees away from the temperature that 4340 steel is tempered at, just sayin!

Even if the rod got to 1150F and air cooled, would it lose its temper? Just asking.

[Shiny]

Originally Posted by track73

Even if the rod got to 1150F and air cooled, would it lose its temper? Just asking.

You would probably reduce the strength significantly at that temperature but time is also a factor.

Considering hardness is a good indicator of strength, here's a chart I found. Note this is probably for a 2-hr hold:



If you want a deep dive, here is a good 4340 heat-treating summary a quick web search found:

https://www.steelforge.com/alloy-steel-4340

I have no clue how 4340 rods are heat-treated but wouldn't be surprised if they were surface-hardened to improve fatigue life. If this is the case, the stress relief of the surface and reduction in fatigue life might be a bigger concern.

[track73]

If the rods are heat treated to the critical temperature (cherry red) for and hour per inch then quenched in an oil bath. They should be tempered at a temp of 450c- 600c then quenched. The tempering takes out some of the brittleness but builds toughness. Getting them to about 550 for a minute or two shouldn't affected them very much if at all.

[Shiny]

Originally Posted by track73

...They should be tempered at a temp of 450c- 600c then quenched....

Thanks... this sounds reasonable. I don't know where 1150 F came from but that is way too hot for a tempering temperature. The OP's photo shows bands of oxide consistent with non-concerning temperatures but hard to tell how hot the small end got.

[track73]

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